Rocky River, West from NPWS Headquarters
2013 Aquatic Ecosystem Condition Report
- Dry in autumn and comprising a flowing stream in spring 2013
- Sparse to moderately diverse macroinvertebrate community in spring when several rare, significant and flow-dependent species were recorded
- Water was fresh, slightly coloured and generally low in nutrients
- Riparian vegetation consisted of native eucalypt forest
About the location
Rocky River is a moderately sized stream within Flinders Chase National Park, located on the western end of Kangaroo Island. The river rises as two main branches at an elevation of nearly 300 m south from the Playford Highway, and flows in a south-easterly direction for about 20 km before merging and ultimately discharging into the Southern Ocean in Maupertuis Bay. The major land use in the 10,256 hectare catchment upstream from the site sampled was nature conservation (98%), with minor areas of wetland, plantation forestry and roads also present. The site sampled was located within the lower catchment off West Bay Road, about 3 km west from the Department for Environment, Water and Natural Resources office and Flinders Chase Visitor Centre.
The river was given a Very Good rating because the site sampled showed no evidence of any significant changes in ecosystem structure and function. There was only some minor evidence of human disturbance due to recreational visits to the banks of the river and stormwater runoff from the unsealed West Bay Rd depositing clays and fine sands into the river.
A sparse to moderately diverse community of at least 19 species of macroinvertebrates was collected or seen from the 4.8 m wide, 50 cm deep river in spring; the river was dry in autumn, apart from a rain-filled puddle that was too small to sample effectively. The river consisted of still to slightly flowing pools connected by faster flowing riffle habitats when sampled in spring. The community was dominated by chironomids (Apsectrotanypus, Procladius, Paramerina and Tanytarsus) and included low numbers of amphipods, mites, springtails, beetles, craneflies, blackflies, mayflies, stoneflies and caddisflies. A number of rare, sensitive and/or flow-dependent species were collected, including the midge (Apsectrotanypus), blackfly (Austrosimulium furiosum), mayfly (Thraulophlebia inconspicua), stonefly (Newmanoperla thoreyi) and caddisfly (Oxyethira columba). The small riffles also provided habitat for a caddisfly (Triplectides) and mosquito larvae, and the presence of crayfish holes in the banks indicated that yabbies also occurred at the site. The wetted area of river was too small to sample in autumn but several caddisflies, mites, dytiscid beetles and mosquito larvae were noted from the shallow pool that was present within the channel. Collectively this indicates that the river supported a range of opportunistic and generalist species, in addition to a number of regionally significant species that favour cool, shaded, freshwater, flowing streams in the State.
The water was fresh (salinity 208 mg/L), slightly acidic (pH 6.56), well oxygenated (65% saturation), slightly coloured, and with generally low concentrations of nutrients such as phosphorus (0.02 mg/L) and nitrogen (0.54mg/L).
The sediments were dominated by sand and detritus, with smaller amounts of cobble, silt, clay and boulder also present on occasions; samples taken from below the surface were grey sands and there was no evidence to indicate that the sediments were anaerobic or lacking in oxygen. There was some evidence of bank erosion from past flood damage extending over nearly 10% of the site in autumn but this was not evident during the follow-up spring survey. No animal droppings were seen in the vicinity of the riverbed; the feral pigs that defaecated in the river and damaged the banks at this site in 2008, showed no indications of any recent visits to the lower Rocky River in 2013.
There was no evidence of any dried filamentous algal mats on the dry sediments of the river and the only aquatic plant seen in the river were water ribbons (Triglochin) that covered more than 10% of channel. The riparian zone was dominated by gums and wattles over bracken and rushes. The surrounding vegetation near the river comprised dense eucalypt woodland within the National Park.
Special environmental features
The river provided habitat for several regionally significant species that included two types of fly (chironomid and blackfly), a mayfly, stonefly and one caddisfly. The location within a national park and general lack of evidence of human disturbance (eg weed and pest species) highlights the importance of this river as an example of a near-natural river for not just the island but the southern part of the State as well.
Pressures and management responses
|Runoff from unsealed roads during high rainfall periods leading to fine sediments discharging into the creek (increasing turbidity and smothering habitat)||This information is not available at the moment but it will be updated as soon as possible.|